Small simplification of MergeTreeDataWriter#17943
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alesapin
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| using SerializationState = IDataType::SerializeBinaryBulkStatePtr; | ||
| using SerializationStates = std::unordered_map<String, SerializationState>; | ||
| /// Count index_granularity for block and store in `index_granularity` | ||
| size_t computeIndexGranularity(const Block & block) const; |
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By the way, index granularity was somewhat confusing to me now that we have secondary indexes. Maybe order_by_granularity or something would be better...
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Actually, order_by_granularity is more confusing because of not all columns from ORDER BY expression stored in primary.idx on disk. Secondary indices granularity calculated in primary index granules. I agree that these interchangeable words like mark, granule, granularity, rows in mark, index granularity and so on are very confusing at first glance.
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In ClickHouse#17120 (that was reverted in ClickHouse#17918 already) marks adjustemnt was introduced, but it may lead to corruption of marks files, that may cause two things: 1) Incorrect marks files, which lead to reading more rows than there are (can be reproduced with `max_threads`>1 or/and `PREWHERE`, and `optimize_move_to_prewhere`) 2) Can't adjust last granule because it has X rows, but try to subtract Y rows (ClickHouse#9260) And 1) is pretty hard to diagnosis, since it does not throw any error, it just may return wrong result. Fortunately both problems can be fixed with `OPTIMIZE TABLE ... [ FINAL]`. Cc: @alesapin Refs: ClickHouse#17943 Refs: ClickHouse#18223
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